1. Field of the Invention
The present invention relates to a process to drain a fibrous pulp suspension that includes feeding a layer of suspension to be drained between two converging surfaces and relatively moving the two surfaces with respect to each other at a desired velocity. In this manner, the suspension may be drained toward both surfaces. The present invention may utilize a draining device including an inner arched surface including a pivoting cylinder having a sleeve with openings, and an outer arched surface including a screen belt guided around a portion of the inner arched surface. The pivoting cylinder may be driven. Alternatively, the screen belt may be an endless belt guided around an non-driven pivoting cylinder. Further, the inner arched surface may include a stationary arched shoe and the outer arched surface may include an endless screen belt moved around a portion of the stationary arched shoe.
2. Discussion of the Background Information
WO 96/08660 describes a device in which a process for draining a fibrous pulp suspension may be performed. This device contains a suction roll that can be driven and includes a permeable surface, a portion of its circumference being surrounded by an impermeable plastic belt. The suspension is inserted between these two surfaces and drained.
Processes of the above-type generally attempt to achieve the best possible drainage with the highest possible throughput. However, the obstacle in achieving this goal is that the impermeable belt in the first part of the draining zone only allows drainage toward one side. In this manner, a substantial vacuum is required to achieve a sufficient drainage capacity and to compensate the centrifugal forces.
Another disadvantage of the prior art is that solid matter can accumulate on the stationary and impermeable screen surface, which and can quickly lead to clumps that can seriously interfere with the proper operation of the entire device. Further, cleaning of these surfaces during operation is not possible.